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Copyright ERS Journals Ltd 1997
European Respiratory Journal
ISSN 0903 - 1936
Eur Respir J 1997; 10: 361–366
DOI: 10.1183/09031936.97.10020361
Printed in UK - all rights reserved
Effect of a bed covering system in children with asthma
and house dust mite hypersensitivity
J.M. Frederick*, J.O. Warner*, W.J. Jessop*, I. Enander**, J.A. Warner*
Effect of a bed covering system in children with asthma and house dust mite hypersensitivity. J.M. Frederick, J.O. Warner, W.J. Jessop, I. Enander, J.A. Warner. ©ERS
Journals Ltd 1997.
ABSTRACT: Allergen avoidance is regarded as an important approach to management of atopic asthma. The effect of Intervent bed covering systems on house
dust mite (HDM) allergen exposure, asthma symptoms and markers of inflammation was investigated in 31 HDM sensitive asthmatic children.
Dust concentrations of Dermatophagoides pteronyssinus allergen 1 (Der p 1) were
monitored before and after covering the mattress, duvet and pillow with active
and placebo covers for 3 months, in a single-blind, cross-over trial. Twice daily
peak expiratory flow rate (PEFR), daily symptom scores and treatment schedule
were recorded. Bronchial hyperresponsiveness was monitored by histamine challenge (provocative concentration of histamine causing a 20% fall in forced expiratory volume in one second (PC20)), and inflammation by measuring eosinophil
cationic protein (ECP), eosinophil protein X (EPX), eosinophil peroxidase (EPO),
and soluble interleukin-2 receptor (sIL-2R) in serum.
There was a significant reduction in Der p 1 when the mattress, duvet and pillow were covered with the active bedding. There was no significant improvement
in symptoms of asthma, PEFR, bronchodilator usage or PC20. Also, ECP, EPX,
sIL-2R concentrations did not change for either treatment. EPO concentrations
were significantly lower in the active compared to the placebo period.
The active bed covers reduced retrievable Dermatophagoides pteronyssinus allergen 1 (Der p 1) from the bedding, with short term clinical benefit.
Eur Respir J 1997; 10: 361–366.
Asthma is the commonest chronic disease of childhood, and has increased in prevalence and severity in
recent years [1, 2]. House dust mites (HDMs) are known
to be a major source of allergens, affecting 50–75% of
atopic asthmatic individuals [3, 4]. Mattresses support
large numbers of mites and their faeces (which contain
the major allergen Dermatophagoides pteronyssinus allergen 1 (Der p 1) [5]. The particles are small (10–40 µm)
and movement in the bed can generate airborne allergen from the reservoir in the bedding.
It has been demonstrated that avoidance of allergen,
e.g. at high altitude where allergen levels are low [6], and
in the domestic environment [7], can be beneficial in the
management of asthma.
Studies to evaluate various types of bedding covers
have demonstrated potential benefits [7–11]. Initial studies used impermeable plastic covers [7–9], and a more
recent study used polyurethane coated covers, but these
covers are rather uncomfortable [10]. A clinical trial in
children demonstrated a significant reduction in miteallergen exposure and subsequent reduction in bronchohyperresponsiveness (BHR) [11]. Further studies are
required to establish the clinical contribution of bed coverings to the treatment of asthma [12].
A fabric called "Intervent" (W.L. Gore Associates,
*Child Health, University of Southampton,
Southampton, UK. **Pharmacia AB,
Uppsala, Sweden.
Correspondence: J.M. Frederick
Child Health
Level G, Centre Block
Southampton General Hospital
Tremona Road
Southampton
SO16 6YD
UK
Keywords: Asthma
barrier bed covers
children
eosinophil proteins
house dust mite
Received: October 30 1995
Accepted after revision October 12 1996
Livingstone, UK), which is water vapour permeable
(pore size 0.1 µm) but HDM allergen impermeable, has
now been developed. Preliminary studies in adults with
allergic rhinitis and asthma produced a significant clinical improvement [13]. A pilot study with Intervent covers established the need to cover the mattress, duvet and
pillow to reduce exposure to Der p 1 [14]. Recently,
markers of eosinophil activation in serum and urine have
been used as clinical assessments of asthma [15, 16].
In childhood asthma, raised serum levels of eosinophilic
cationic protein (ECP) decreased with treatment [17,
18]. Also, serum ECP and eosinophil protein X (EPX)
concentrations in asthmatic children changed significantly in association with exposure to, and avoidance
of, allergens [19]. Additionally, elevated serum soluble
interleukin-2 receptor (sIL-2R) (T-cell marker) concentrations have been demonstrated in asthma, which decrease with treatment [20].
This study investigated the effectiveness of Intervent
bed covers in reducing Der p 1 exposure of HDM sensitive asthmatic children, with clinical symptoms monitored by lung function testing, peak flow measurements
and diary cards, and disease activity by serum ECP,
EPX, eosinophil peroxidase (EPO) and sIL-2R concentrations.
J.M. FREDERICK ET AL.
362
Materials and methods
Subjects
Thirty one atopic asthmatic children (11 females and
20 males) aged 5–15 (mean 9) yrs were recruited from
the Southampton General Hospital Paediatric asthma
clinic from November 1992 to July 1993, i.e. 8 months.
Informed consent was obtained from the legal guardians of all patients, and the study was approved by the
Southampton University Hospitals Joint Ethics Committee. All patients had either a positive skin-prick test to
HDM (≥4 mm in diameter) and/or specific immunoglobulin E (IgE) to HDM (radioallergenosorbent test (RAST)
≥grade 3), and a documented history of perennial asthma. Pharmacotherapy was administered following the
step-up schedule as outlined in the Paediatric Asthma
Consensus Group publication [21]. Twenty nine patients had required prophylactic treatment (3 with sodium cromoglycate and 26 with inhaled steroids) as well
as bronchodilator therapy, while two patients used bronchodilator alone (one male aged 5 yrs and one female
aged 13 yrs). The duration of the study was 1 year (November 1992 until November 1993). The median forced
expiratory volume in one second (FEV1) as a percentage of predicted for height was 78%, with 16 of the 31
children having a FEV1 <80% pred.
Bed covers
Zippered Intervent covers (W.L. Gore, Livingstone,
UK) or placebo polycotton covers for the mattress, duvet
and pillow were used according to the protocol.
Protocol
This was a single-blind, cross-over study. After a 2
week run-in period, the 31 patients were randomly assigned to two groups (in order of recruitment). Group 1 (16
patients) received active bed covers, and Group 2 (15
patients) received placebo bed covers. These remained in
situ for 3 months (Period 1), during which time they were
asked to wipe down the active covers with a damp cloth,
once a week (to remove settled dust). The covers were then
removed and there was a wash-out period of 1 month.
Group 1 then received placebo covers and Group 2
active covers, for a further 3 months (Period 2).
Dust sampling
Dust samples were collected at Baseline 1, at the end
of Period 1, end of wash-out period (Baseline 2), and
at the end of Period 2.
These samples were taken from the whole area of the
mattress (3 min), duvet (5 min) and pillow (5 min) using a Hoover dustette vacuum cleaner, adapted so that
individual dust samples could be obtained using a standard collecting device (ALK, Denmark).
Dust Der p 1 analysis
For antigen determination, dust samples were extracted in phosphate-buffered saline (PBS) containing 0.5%
Tween 20 and 0.2% bovine serum albumin (BSA) overnight (1:5 weight/volume). Samples were filtered (Anotop
10 plus, 0.2 µ; Whatman, Maidstone, UK) and analysed
by means of an enzyme-linked immunosorbent assay
(ELISA) system for Der p 1, performed according to
the manufacturers' recommendations (ALK Laboratories,
Denmark).
Diary cards
Patients recorded symptom scores, medication, and
peak expiratory flow rate (PEFR) as measured with a
mini-Wright peak flow meter. PEFR was recorded before
breakfast and bedtime medicines, the best of three blows
being measured on each occasion. Symptoms were scored as follows: asthma last night (ALN) (0–3), daytime
wheeze (DW) (0–3); and exercise tolerance (ET) (0–3).
Consumption of inhaled bronchodilators, corticosteroids, sodium cromoglycate, and other medications was
also recorded. Diary cards were completed for a run in
period of 2 weeks, and throughout the trial. Average
morning and evening PEFRs were calculated, and an
average daily score for symptoms and bronchodilator
use (over the last 2 weeks of each study period).
Lung function
Lung function tests were performed at Baseline 1 and
at the end of Periods 1 and 2, using a Vitalograph compact spirometer (Buckingham, UK). When the patients had
optimised their technique, the best of three flow-volume
loops was taken for the calculation of baseline FEV1 as
a percentage of predicted for age, height, and sex matched controls. The tests were performed after withholding
all β2-agonist medication for 12 h. Reference values for
lung function tests were taken from the data of POLGAR
and PROMADHAT [22]. Patients then performed an inhalation provocation test with histamine acid phosphate using
a standard modification of Cockroft's method [23]. A 2
min tidal volume breathing technique was used for inhalation, followed by spirometry at 0.5, 1.5 and 3 min. Calibrated Intersurgical Cirrus nebulizers (Berkshire, UK) were
used, filled with 4 mL histamine solution in doubling
dilutions. Provocation concentrations for a 20% drop in
FEV1 (PC20) were calculated and log transformed.
Blood assays
Blood samples were drawn at Baseline 1 and at the
end of Periods 1 and 2 using a 21-gauge butterfly needle with syringe attached, taking care to avoid haemolysis (thus potentially damaging the eosinophils). These
were then transferred (needle removed) to unstoppered
SST Vacutainer tubes with clot activator. They were
allowed to stand for 60 min and then centrifuged at
3,500 rpm for 10 min. Serum was removed and aliquots
stored at -80°C until analysis.
ECP was measured by a fluorescent enzyme immunoassay (FEIA) using the Pharmacia CAP™ system (Pharmacia AB Diagnostics, Uppsala, Sweden). EPX was measured
using a Pharmacia Radioimmunoassay (RIA). EPO was
measured by I. Enander at Pharmacia, using a prototype
FEIA on the CAP™ system. sIL-2R was measured by
ELISA (T-cell Diagnostics, Cambridge, USA).
A B E D C O V E R I N G S Y S T E M F O R A S T H M AT I C C H I L D R E N
Statistical analysis
The Mann Whitney U test was performed on the period differences between Groups 1 and 2 to determine
the equality of the active and placebo bed covers. The
Kruskal-Wallis test was performed on the diary card
data on the difference between the baseline and the folTable 1. – Skin-prick test results to common allergens
in 30 patients (positive ≥4 mm wheal)
Allergen
Pts
n
Allergen
HDM
Feathers
Cat
Dog
Horse
Grass
30
7
19
9
4
16
Tree
Alternaria
Cladosporium
Egg
Peanut
Pts: patients; HDM: house dust mite.
Pts
n
2
1
2
1
2
363
lowing months. Statistical significance was achieved
when p-value was equal to or less than 0.05 (95% confidence interval (95 CI%)).
Results
Patients skin-prick test results to common allergens
are recorded in table 1. Only one patient was monosensitive to HDM. Fifty percent of the patients were
sensitive to pollens. Of these patients, 50% were exposed
to a pollen season during the active period (but not in
the last month alone), and 50% during the placebo period of the study. Many of the children were sensitive to
animals, and 7 of the 31 patients were exposed to a pet
they were sensitized to during the whole study period.
Three patients were taking regular sodium cromoglycate (2 males and 1 female, aged 5–6 yrs), 26 inhaled
corticosteroids (18 males and 8 females, aged 5–15 yrs)
and two were using bronchodilators only (1 male aged
5 yrs and one female aged 13 yrs).
Table 2. – Weight of dust (g or g·m-2 area sampled) and concentration of Der p 1 allergen (ng·g-1 or ng·m-2 area
sampled) in dust retrieved from bedding (at baseline and end of washout period), with active or placebo covers (in
situ), for both arms of the study: Group 1 = Active → Placebo; Group 2 = Placebo → Active
Gp Dust
Baseline 1
Period 1
Active
Mattress
Duvet
Pillow
Mattress
Duvet
Pillow
1 Weight
0.175
0.111
0.084
0.049
0.02
0.021
g
(0.051–0.791)
(0.014–0.449)
(0.013–0.408)
(0.003–0.187)
(0–0.06)
(0–0.038)
Weight
0.102
0.04
0.127
0.029
0.006
0.029
(0.032–0.463)
(0.004–0.166)
(0.014–0.648)
(0.002–0.131)
(0–0.022)
(0–0.06)
g·m-2
Der p 1
12403
20639
10855
1246
0
0
(616–24138)
(558–110000)
(878–32500)
(0–66667)
(0–62500)
(0–27727)
ng·g-1
Der p 1
863
505
1364
50
0
0
ng·m-2
(64–7891)
(22–9696)
(137–11657)
(0–3625)
(0–3719)
(0–645)
Placebo
2 Weight
0.193
0.088
0.063
0.131
0.081
0.06
g
(0.026–1.177)
(0.014–0.393)
(0.006–0.145)
(0.015–0.59)
(0.034–0.179)
(0.02–0.128)
Weight
0.116
0.031
0.103
0.077
0.03
0.121
(0.015–0.83)
(0.005–0.146)
(0.01–0.23)
(0.011–0.414) (0.009–0.067) (0.032–0.324)
g·m-2
Der p 1
14759
23418
27586
13500
6879
5167
(0–82500)
(1095–67500)
(398–1283333)
(900–63830)
(559–77419)
(0–63158)
ng·g-1
Der p 1
1617
525
2582
1287
204
794
(5–42263)
(33–9825)
(65–12222)
(33–6316)
(5–13333)
(0–11111)
ng·m-2
Baseline 2 (wash-out)
Period 2
Placebo
1 Weight
0.248
0.126
0.087
0.145
0.106
0.054
g
(0.053–0.692)
(0.065–0.276)
(0.017–0.221)
(0.07–0.667)
(0.047–0.185) (0.009–0.272)
Weight
0.161
0.044
0.127
0.102
0.038
0.092
(0.031–0.403)
(0.024–0.102)
(0.027–0.289)
(0.041–0.39)
(0.017–0.069) (0.014–0.288)
g·m-2
Der p 1
7275
5715
7250
2737
4135
7779
(100–30519)
(461–25325)
(288–70588)
(53–97143)
(468–21667)
(707–93333)
ng·g-1
Der p 1
1095
248
1000
190
127
563
(12–3177)
(11–722)
(54–11746)
(8–3977)
(19–722)
(46–4505)
ng·m-2
Active
2 Weight
0.38
0.113
0.092
0.047
0.017
0.015
g
(0.05–0.655)
(0.056–0.293)
(0.034–0.177)
(0–0.097)
(0–0.063)
(0–0.058)
Weight
0.235
0.04
0.158
0.026
0.006
0.024
(0.035–0.460)
(0.021–0.109)
(0.054–0.327)
(0–0.057)
(0–0.023)
(0–0.105)
g·m-2
Der p 1
8500
10429
19210
1086
0
0
(354–50000)
(277–29737)
(46–621747)
(0–6452)
(0–2231)
(0–3333)
ng·g-1
Der p 1
1058
425
2143
35
0
0
(17–17824)
(7–2654)
(12–17460)
(0–234)
(0–21)
(0–79)
ng·m-2
Values are expressed as median, and range in parenthesis. Der p 1: Dermatophagoides pteronyssinus allergen 1; Gp: group.
J.M. FREDERICK ET AL.
364
Der p 1 concentrations
The weight of dust (g), or g·m-2 area sampled, and
concentration of Der p 1 (ng·g-1) and (ng·m-2 area sampled) for Groups 1 and 2 are summarized (median and
range) in table 2. There was a significant decrease in
the concentration of Der p 1 (ng·g-1) in the recoverable
dust from the mattress (p=0.0012), duvet (p<0.0001)
and pillow (p<0.0001) after the addition of active bed
covers compared to placebo covers (fig. 1); and also, if
expressed as ng·m-2 (p≤0.0001 for mattress, duvet and
pillow).
Diary card analysis
Diary card analysis indicated that the baselines for
the active and placebo periods were significantly different, and so all subsequent data had to be compared
1,000,000
p=0.0012
p<0.0001
p<0.0001
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Lung function
The range of PEFR at baseline was 55–113% pred
(median 84% pred). The range of FEV1 at baseline was
43-105% predicted (median 78%). There was no significant difference in FEV1 (p=0.6) after the active bed covers (median 85% pred, range 53–114% pred) compared
to their baseline (median 86% pred, range 43–123% pred).
Also, PC20 histamine showed no significant difference
(p=0.15) between the active (median 0.3 mg·mL-1, range
0.05–2.1 mg·mL-1) and placebo (median 0.4 mg·mL-1,
range 0.05–2.6 mg·mL-1) treatments.
Blood samples
■
Der p 1 concentration ng·g-1 dust
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1,000
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10,000
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100,000
to their own baseline (table 3). There was no significant improvement in symptoms of asthma during the
active and placebo periods of the study, although from
the figures, there is a suggestion of an improvement in
symptoms of daytime wheeze and exercise tolerance
during the first two months with active covers in situ.
There was no significant improvement in symptoms
during the placebo period of the study. There was no
significant change in PEFR or bronchodilator usage
between the two periods. There was, however, a trend
for evening PEFR to improve in the active group (p=
0.09) after the first two months of the study. Similarly
the morning PEFR showed a trend to improve in the
placebo group after three months (p=0.08).
■
100
■
■
10
(10)
Placebo Active
Mattress cover
■
(25)
(28)
(2)
■
■
■
0.1
Placebo Active Placebo Active
Duvet cover
Pillow cover
Fig. 1. – Dermatophagoides pteronyssinus allergen 1 (Der p 1) concentrations (ng·g-1) in the mattress, duvet and pillow after 3 months
with active and placebo bed covers in situ. Median values are shown
by horizontal bars. Values in parentheses represent the number samples with undetectable levels of Der p 1.
Blood samples were obtained from 30 of the 31 patients
on all three occasions. One patient consistently refused
blood sampling (a female aged 6 yrs).
Currently, there are few published data on paediatric
ranges for the eosinophil proteins [24], and the present
results have been compared to normal healthy adults
values. The range of ECP in these patients at baseline
was <2–43.3 µg·L-1 (mean 13.4 µg·mL-1), with nine patients above the upper limit for adults. The range of EPX
in these patients at baseline was 14–171 µg·L-1 (mean
53.8 µg·mL-1), with 20 patients above the upper limit
for adults. The range of EPO in these patients at baseline was 0.8–146 µg·L-1 (mean 34.3 µg·L-1), with 22
patients above the upper limit for adults. At baseline,
there was no significant difference in the EPO levels in
Table 3. – Daily average (last 2 weeks of each month) of symptom scores (0–3) and daily medication (µg β2-agonist), from diary cards for each of the 3 months using active and placebo bed covers compared to the baseline
Diary
Baseline
Active
Baseline
Placebo
Month 1
Month 2
Month 3
Month 1
Month 2
Month 3
ALN score
0.2
0.1
0.07
0.1
0.09
0.1
0.03
0.09
(0–1.9)
(0–0.9)
(0–0.8)
(0–0.8)
(0–2.5)
(0–2.4)
(0–1.7)
(0–1.7)
DW score
0.4
0.3
0.3
0.3
0.3
0.2
0.1
0.2
(0–1.2)
(0–1.1)
(0–1.1)
(0–1.1)
(0–2.1)
(0–2.2)
(0–1.6)
(0–1.1)
ET score
0.4
0.2
0.2
0.2
0.2
0.2
0.1
0.2
(0–1.6)
(0–1.1)
(0–1.1)
(0–1.1)
(0–2.1)
(0–2.2)
(0–1.6)
(0–1.2)
262
255
263
257
269
264
272
282
PEFR a.m. L·min-1
(132–389)
(137–407) (155–379)
(177–391)
(141–390) (154–432) (158–431) (155–428)
265
277
290
258
274
283
301
307
PEFR p.m. L·min-1
(142–402)
(141–416) (147–396)
(174–407)
(160–418) (159–431) (164–428) (167–432)
Medication µg
120
60
80
80
60
60
20
40
(0–986)
(0–816)
(0–634)
(0–312)
(0–542)
(0–816)
(0–490)
(0–372)
Values are median, and range in parenthesis. ALN: asthma last night; DW: daytime wheeze; ET: exercise tolerance; PEFR: peak
expiratory flow rate.
A B E D C O V E R I N G S Y S T E M F O R A S T H M AT I C C H I L D R E N
250
EPO concentration µg·L-1
p=0.02
200
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150
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■
100
50
0
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■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
Active covers
Placebo covers
Fig. 2. – Serum eosinophil peroxidase (EPO) concentration (µg·L-1)
after 3 months with active or placebo bed covers. Horizontal bars
show median values.
those patients going into Group 1 (range 0.8–72 µg·L-1,
mean 26.1 µg·L-1) or Group 2 (range 0.9–146 µg·L-1,
mean 43.7 µg·L-1).
There were significantly lower levels of EPO (p=0.02)
after the active bed covers had been in situ compared
to the placebo bed covers (fig. 2). Although there seemed
to be some trend for the levels of ECP and EPX to be
lower after active bed covers compared to placebo covers, this was not significant (p=0.16 and p=0.19, respectively). The range of sIL-2R in these patients at baseline
was 189–907 U·mL-1 (median 600 U·mL-1) i.e. none were
above the upper level for healthy children in this age
range [25]. There was no difference (p=0.33) in sIL-2R
after the addition of active compared to placebo covers.
Discussion
Most previous studies of allergen avoidance involving
barrier bed covers have looked at mattress dust alone
and have not considered the contribution of the dust
reservoirs present in other items of bedding. These undoubtedly add to the allergen pool in the bedroom environment. Our previous study showed that, due to high
Der p 1 concentrations in the various items of bedding,
covering the mattress alone is not sufficient to significantly reduce Der p 1 exposure [14].
Although the first International Workshop on dust
mite allergy [26] suggested that 10 µg·g-1 is a risk factor for acute asthma in mite allergic people, 87% of our
patients had concentrations greater than this in at least
one item of their bedding, and they were not all suffering from acute asthma. This suggests either that they
were well-controlled by medication or that the threshold is inappropriate for the UK. The third International
Workshop (Cuenca, Spain 1995) decided that the relationship between exposure and symptoms of asthma
among sensitized individuals is very complex, and a
simple threshold for symptoms is inappropriate (PlattsMills TAE, personal communication). The Intervent bed
covers significantly reduced both the concentration of
allergen and amount of dust retrieved from the bedding
compared to the placebo covers. However, with the placebo covers, there was a significant reduction in the Der
365
p 1 concentration (ng·m-2) retrieved from the pillow,
with a tendency to decrease in the mattress also. This
did not, however, result in significant clinical benefit,
but there was a trend for improvement in morning PEFR
by the end of 3 months with placebo covers. This suggests that even the placebo had a beneficial effect in
preventing release of allergen into the air.
There was some indication that an improvement in
some symptoms of asthma may have been achieved with
the active bed covers over the first two months of the
study, but these were of minor magnitude and there was
a large range in the data. A larger study would be required
to investigate this further. These results imply that the
effectiveness of the measure, if any, is short-lived. Clearly, there are many other sources of allergen which may
confound the results. However, as a single intervention
the results are promising, and the incorporation of Intervent bed covers into a multisystem avoidance programme may provide more successful results. We also
hypothesize that the allergen levels may actually increase
in the carpet around the bed whilst using the active bed
covers, as skin scales will accumulate on the surface of
the cover (that would normally have gone into the mattress) and be swept onto the floor. More frequent damp
wiping of the covers may be required. This could account
for the loss of effect after 2 months. Unfortunately, we
did not collect dust samples from the carpet and this
would be advisable in future studies on bed covers.
Many factors will mitigate against a single allergen
avoidance intervention achieving significant benefits,
and a number were operative in the present study. Fifty
percent of the patients were sensitized to pollens, though
the exposure was comparable between the groups, and
25% of the patients were exposed constantly to an animal to which they were sensitized. Undoubtedly, viral
infections will also have played a role in aggravating
asthma and we could not assess their contribution to the
outcome, as this is only possible with very expensive
technology.
The histamine challenge test did not demonstrate an
improvement in the active group but its value as a monitor of clinical change has come under much scrutiny
recently [27]. Little change, however, was observed in
twice daily PEFR. As all patients were reasonably controlled on regular prophylactic therapy, it was probably
unreasonable to expect much change in these parameters.
The serum eosinophil proteins declined after the addition of active bed covers, with the fall in EPO being significant. There is selective release of different proteins
from eosinophils, and TOMASSINI et al. [28] have demonstrated EPO release after IgE stimulation, whereas
ECP release was demonstrated with anti-immunoglobulin G (IgG) monoclonal stimulation. CARLSON et al.
[29] have also shown a significant rise in ECP and EPX
in pollen-atopic patients with asthma during the pollen
season. There is, however, a more rapid and 10 fold
more significant rise in EPO in this group [30]. sIL-2R
showed no change after either type of bed covers.
However, as none of the patients in this study had elevated levels on recruitment, this is perhaps not surprising. We have shown that this T-cell marker decreases,
only very slowly, with long-term allergen avoidance at
high altitude [31].
J.M. FREDERICK ET AL.
366
Overall, we believe that this study has demonstrated
that there is a decrease in serum eosinophil peroxidase
amongst a group of well controlled asthmatics using
Intervent bed covers, coincident with a decrease in recoverable Dermatophagoides pteronyssinus allergen 1 (Der
p 1) from the bedding. However, it is likely to be necessary to follow other house dust mite avoidance measures, such as the removal of carpets (particularly the deep
pile type), improved ventilation and decreased humidity, in order to obtain a more persistent and greater effect.
Barrier bed covers, however, offer one of the simplest
and most effective approaches to reduction of house dust
mite allergen exposure in asthmatic children, and should
be considered the first approach to allergen avoidance.
Acknowledgements: We would like to thank W.L.
Gore for funding JMF and WJJ and for providing the
"Intervent" bedding covers for the study. They would
also like to thank the National Asthma Campaign and
the British Lung Foundation for funding JAW, and
Pharmacia AB (Sweden) for providing assays kits for
ECP, EPX, and for measuring EPO.
14.
15.
16.
17.
18.
19.
20.
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